1. Field of Invention
The invention relates to the construction of a piezoelectric ink-jet printer head and a method of fabricating same.
2. Description of Related Art
An on-demand type piezoelectric ink-jet printer head is disclosed in U.S. Pat. No. 4,680,595. The disclosed head includes a nozzle plate having a plurality of nozzles, and a channel plate having chambers each associated with each of the nozzles. A diaphragm plate is bonded using an adhesive to the back of the channel plate. Transducers are secured to one side of the diaphragm plate so as to be aligned with the pressure chambers.
The diaphragm plate is made of a thin metal plate with a thickness of 25 xcexcm or less in order to efficiently transmit the deformation of the transducers.
In order to vibrate the diaphragm plate together with the transducers, the transducers should be bonded onto the diaphragm plate. However, the diaphragm plate, which is extremely thin, makes a bonding operation difficult.
In addition, the diaphragm plate is 25 xcexcm or less in thickness, and thus its rigidity is very low. Accordingly, when any transducer deforms to change the pressure in the pressure chamber, the diaphragm plate itself generates vibrations separately from the transducer. To eliminate the influence of such vibrations, the transducer driving cycle should be elongated. Consequently, the transducers cannot be driven at high frequencies, resulting in a prolonged ink ejection cycle and a low print speed.
An ink-jet head disclosed in Japanese Laid-Open Patent Application No. 4-341851 addresses the above problems. The disclosed head includes a nozzle plate having a plurality of nozzles, a cavity plate having pressure chambers each associated with each of the nozzles, and a plate type piezoelectric actuator. The piezoelectric actuator is constructed by laminating piezoelectric sheets, each sandwiched by flat individual electrodes formed in a one-to-one correspondence with the pressure chambers and a common electrode shared by the pressure chambers. The individual electrodes are electrically insulated from the common electrodes by each of the piezoelectric sheets. The piezoelectric sheets are laminated such that the individual electrodes are aligned with the associated pressure chambers.
In this construction, the lowermost piezoelectric sheet is bonded to the cavity plate at portions other than the pressure chambers such that the lowermost piezoelectric sheet covers the pressure chambers. The piezoelectric sheets are made of ceramic and are likely to absorb water.
Accordingly, when the ink-jet head is used for a long time, the lowermost piezoelectric sheet absorbs water content contained in the ink guided to the pressure chambers, and electrical insulation between the individual electrodes and the common electrode is damaged.
To solve such a problem, interposing a synthetic resin diaphragm plate between the lowermost piezoelectric sheet and the cavity plate is conceivable. However, because a synthetic resin diaphragm plate is far less rigid than a metal diaphragm plate, driving the ink-jet head at high frequencies becomes much more difficult.
The invention involves providing an adhesive or an adhesive sheet between the piezoelectric actuator and the cavity plate of an ink-jet printer head and a method of manufacturing an ink-jet printer head.
The ink-jet printer head has a plate type piezoelectric actuator and a metal cavity plate with pressure chambers. The piezoelectric actuator overlies the metal cavity plate and they are connected together using an adhesive sheet or simply an adhesive. The adhesive sheet covers the pressure chambers, but does not attach to the pressure chambers. It is made of an ink-impermeable resin and electrically insulative material, such as: a film of polyamide base hotmelt adhesive, a film of dimer-acid base polyamide resin, and a film of polyester base hotmelt adhesive. Instead of using an adhesive sheet, a polyolefin base hotmelt adhesive may be used.
The cavity plate includes a base plate, a nozzle plate, manifold plates and a nozzle plate. Optionally, one or more spacer plates may also be provided.
The base plate also has pressure chambers, each of the chambers has an end passage. The chambers are arranged from the base plate to form two rows so that opposed end passages of the pressure chambers are disposed in an interlaced relationship. The pressure chambers extend in a lateral direction of the base plate. Additionally, the base plate has a longitudinal central axis which defines two base plate portions, a first longitudinal reference line on one side of the longitudinal central axis, and a second longitudinal reference line on the opposite side of the longitudinal central axis. One row of the pressure chambers is disposed on one base place portion so the end passages are aligned with the longitudinal reference line on the opposite base plate portion, and the other row of pressure chambers is disposed on the other base plate portion so that the end passages of its row of chambers are aligned with the other longitudinal reference line. The base plate also includes an ink supply hole in each of the base plate portions.
The nozzle plate has a plurality of nozzles arranged in a first row and a second row in a longitudinal direction of the nozzle plate, so that the first row of nozzles is staggered from the second row of nozzles. Each nozzle corresponds to a pressure chamber end passage.
One or more manifold plates may be provided. Preferably however two manifold plates are provided. The first manifold plate is disposed between the base plate and a second manifold plate and contains a first ink passage in the shape of an elongated opening. The second manifold plate contains an ink passage having the same elongated shape as the first ink passage. However, it is recessed within the plate and does not penetrate through the plate.
The base plate, nozzle plate and manifold plate are laminated together so that each end passage of the pressure chambers is aligned with a corresponding nozzle and with the manifold plate through holes.
A spacer plate with a first and second set of apertures and a first and second spacer plate ink supply hole may be provided. The first set of apertures is disposed in the spacer plate to form a first and second row of through holes with each row being disposed in a longitudinal direction of the spacer plate. Also, the first row of through holes is staggered from the second row of through holes. The second set of apertures includes larger through holes disposed in the space plate to form rows of larger through holes.
The plates are laminated together so that ink flows through the ink supply hole into the manifold plate ink supply passages then through the rows of larger through holes and into the pressure chambers. Ink discharges through the end passages of the pressure chambers and through corresponding nozzles in the nozzle plate.
The actuator includes a first set of piezoelectric sheets and a second set of piezoelectric sheets. The first set of piezoelectric sheets has individual electrodes formed in rows, dummy common electrodes disposed thereon and through holes formed therein. The second set of piezoelectric sheets has a common electrode, lead portions formed in the common electrode, dummy individual electrodes and through holes formed therein.
The actuator includes a first sheet and a second sheet. The first sheet has sets of surface electrodes and through holes formed therein. The second sheet has individual electrodes and dummy common electrodes. The sheets are laminated together to form a stack so that the individual electrodes, the dummy electrodes and the first set of electrodes are vertically aligned and electrically connected with each other and so that the common electrodes, the dummy common electrodes and the second set of surface electrodes are vertically aligned and electrically connected. Additionally, the through holes are filled with a conductive material.
When an electrical potential is applied to the actuator, it causes the actuator to deform to increase the volume of the pressure chambers, thereby causing ink to flow into the pressure chambers. When the electrical potential is removed, the actuator returns to its original state and decreases the volume of the pressure chambers. The adhesive or adhesive sheet expands and contracts as the actuator deforms.
The method of manufacturing an ink-jet printer head involves providing a cavity plate and an actuator, applying an adhesive sheet or an adhesive to the bottom surface of the actuator, then pressing the cavity plate and actuator together. Additionally, the method includes covering the cavity plate pressure chambers with the adhesive sheet, but not attaching the adhesive sheet to the pressure chambers. The method also includes providing a base plate, a nozzle plate and a manifold fold, and laminating them together to form the cavity plate described above.
It is an object of the invention to provide an ink-jet printer head with improved overall rigidity that does not generate vibrations, so that it is easier to drive the ink-jet head at high frequencies. Additionally, it is another object of the invention to provide an adhesive sheet that expands and contracts with a piezoelectric actuator, that prevents ink leaks from developing between the piezoelectric actuator and cavity plate, and firmly secures the piezoelectric actuator to the cavity plate.
Another object of the invention is to provide a method of economically manufacturing ink-jet printer heads with reduced vibrations so that ink-jet printer heads can be driven at high frequencies.